Detacking apparatus

ABSTRACT

The removal of a flexible sheet from sheet transport devices is facilitated by applying a varying electrical field between the flexible sheet and an electrical conductor coated with a dielectric material.

United States Patent 11 1 Gibbons Oct. 14, 1975 [54] DETACKING APPARATUS 3,508,824 4/1970 Leinbach et al. 271 1310. 3 1 1 Inventor: Carl Gibbons, Rochester, NY 3:252:32 1133; 23221121113311: :13: iii/Bi 5 3 Assigneez Eastman Kodak Company, 3,811,821 5/1974 Ariyama et al. 432/60 Rochester, NY.

[ Filed: Jan- 1974 Primary Examin erEvon C. Blunk ['21] AppL No; 430,265 Assistant Exam'iherBr11ce H. Stoner, Jr.

Attorney, Agent; or Firm-D. I. Hague [52] US. Cl. 271/174; 226/94; 27l/DIG. 2; 27l/DIG. 3 [51] Int. Cl. B65H 29/56 [57] ABSTRACT [58] Field of Search 271/174, 80, DIG. 2, 18.1, DIG 355/3 The removal of a flexible sheet from sheet transport 118/60 devices is facilitated by applying a varying electrical field between the flexible sheet and an electrical con- References Cited ductor coated with a dielectric material.

UNITED STATES PATENTS 2,576,882 11 1951 Koole et al. 271 1310. 3 6'C1aims, 1 Drawing Figure US. Patent Oct. 14, 1975 3,912,257

DETACKING APPARATUS BACKGROUND OF THE INVENTION The present invention relates to sheet handling apparatus and, more particularly, to apparatus for detacking electrically charged sheets from such sheet handling apparatus.

As paper sheets move through sheet manipulation or handling machinery static electricity is generated by friction and by the separation of surfaces. These electrically charged paper sheets have a tendency to stick to and wrap around the machine surfaces which they contact causing breakage and delay. To allow the sheet handling machinery to operate efficiently and at a desirable rate of speed it is necessary, therefore, to prevent the paper sheets from wrapping around the machine surfaces.

To separate the paper sheets from various sheet handling devices, the prior art has employed both mechanical and electrostatic means. One mechanical approach is to wedge the paper sheet from the handling apparatus with stripping fingers. Stripping fingers, however, have a tendency to damage or rip the paper sheet and to scratch and abrade the sheet handling machine surfaces. An air puffer, another mechanical approach used to achieve separation, requires the use of relatively high pressure air to overcome the attraction of the sheet for the sheet handling machinery. However, the strong puffs of air required cause problems in certain applications. For example, in electrophotography, the air puffs create toner dust problems throughout the copying machine.

Prior. art electrostatic techniques neutralize the charge on the paper sheet, for example, by contacting the sheet with a bias roller or by corona discharge. While effective in performing the function of preventing the paper sheet from wrapping about the machine surfaces, electrostatic neutralization techniques cannot control the position of the sheet as it moves away from the contacting surface. As a result, the sheet may become misaligned on the feed path and jam the machinery.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a simple and reliable apparatus for attracting the leading edge of a flexible sheet away from a sheet handling mechanism toward which it is attracted.

Another object of the invention is to provide an apparatus for guiding an electrically charged flexible sheet away from a sheet handling or transport mechanism toward which it is attracted and along a predetermined path.

These and other objects of the invention are accomplished by positioning an insulator-coated electrode iri the vicinity of the exit of a sheet handling apparatus and applying a periodically varying electrical potential to such electrode. The applied potential develops an electrical field between the electrode and the flexiblev sheet producing a force of attraction between them. Since the applied potential varies, the attraction periodically develops to a peak providing a series of electrostatic pulls that attract thesheet away from the sheet handling apparatus. Since the sheet is attracted toward the insulator coated electrode, theelectrode is positioned along the desired output path to guide the movement of the sheet from the handling apparatus to such path.

In accordance with a preferred embodiment of the invention, the sheet handling apparatus comprises a pair of rotatably mounted transport rollers which advance the flexible sheet through the nip formed by the curved surfaces of the rollers. An elongated insulator coated electrode .is positioned substantially parallel to the axes of rotation of the transport rollers and in close proximity to the roller surface toward which the leading edge of the flexible sheet has a tendency to become wrapped around. A periodically varying electrical potential is applied between the electrode and the flexible sheet, the potential being regulated so that no arcing occurs between the electrode and the flexible receiver sheet.

A remarkable feature of the preferred form of the invention is that utilization of a varying electrical potential permits substantially higher peak fields of-attraction to be applied to the'sheet than can be obtained with the use of a constant potential. These higher peak fields in turn give a much better detacking effect than that obtained with a constant but lower potential electric field.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a fragmentary, cross-sectional view of a roller fusing apparatus constructed in accordance with the teachings of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the detailed description of the preferred embodiment which follows, the invention is described in connection with the roller fusing station of an electrophotographic copying machine. It is to be understood, however, that the apparatus of the present invention could be used in other flexible sheet processing apparatus, and, therefore, that the following description of the apparatus related to but not forming part of the invention is provided for illustrative purposes only.

In the practice of electrography, electroscopic marking particles, commonly known as toner, are selectively deposited on the surface of an electrographic recording element to render visible a latent electrostatic image-carried thereon. The toned image is commonly transferred to a paper receiving sheet by applying to the sheet a DC. charge that attracts the toner particles from the recording element to the receiving sheet. The transferred toner image is then fixed on the receiving sheet by a fusing operation.

Referring now to the drawing, a roller fusing device wherein the invention is particularly useful is shown to comprise a compliant, heated fusing roller 2 and a mating backing roller 4. The curved surfaces of the rollers 2 and 4 form a nip 5 from which a flexible receiver sheet 6, bearing a fused toner image onthe side facing fusing roller 2, exits after completion of a conventional fusing operation. Statically generated charges carried on the sheet 6 attract the sheet to the roller 2 so that the sheet tends to follow the roller 2 and become wrapped therearound. And when electrostatic charging is used in the transfer operation as described above, the tendency for the toner bearing surface of the receiving sheet 6 to stick to the fusing roller 2 is greatly increased because the transfer charging increases the attraction of the receiving sheet to the fusing rollers.

Positioned within the nip 5 as close as possible to the non-image bearing side of the receiver sheet 6 is an elongated member 8 that extends in a direction susbstantially parallel to the axes of rotation of the rollers 2 and 4. While the member 8 should be positioned in the nip 5 close enough to the receiver sheet 6 to exert an electrical attraction on such sheet as described in detail hereinafter, its spacing therefrom is not critical to the operation of the invention. In the preferred embodiment illustrated in the drawing, the member 8 is positioned approximately 0.125 inch from the backing roller 4. to assure adequate clearance for the receiver sheet 6 between the member 8 and fusing roller 2, but it is to be understood that other spacings may be used depending upon the particular machine design employed.

Member 8 is made of an electrically conductive material, for example a steel rod 0.045 inch in diameter, and is coated with a dielectric material 12, for example, Teflon, approximately 0.001 to 0.1 inch in thickness, and preferably-approximately 0.010 inch in thickness. Teflon is a trademark of E l DuPont de Nemours and Company and used to designate a plastic consisting of a tetrafluoroethylene polymer. A source of periodically varying electrical potential 10 such as a pulsed DC. or A.C. source, is connected to the conductive portion of member 8. Source 10 applies a potential from to 12 kilovolts, and preferably approximately l0 kilovolts, AC. to member 8 which builds a field on each half cycle that pulls the leading edge of the receiver sheet 6 from the fusing roller 2 and guides the sheet onto the transport conveyor 16.

To insure separation of the leading edge of the receiver sheet 6 from the fusing roller 2, the source of varying potential 10 should, as a lower minimum of operating frequency, complete at least one full cycle by the time the leading edge of the sheet 6 advances from the nip to a position over the member 8. The upper maximum of operating frequency of the varying source is governed by the time it takes to move out any ions present in the gap 14 between the member 8 and roller 2 when the air in the gap breaks down due to the applied field. In the preferred embodiment illustrated in the drawing, the ions are moved out of the gap 14 by the time the source 10 completes approximately onethird of a cycle. From the foregoing, it will be clear to those skilled in the art that the optimum operating frequency of the source 10 can be readily calculated for any given geometry of the sheet handling mechanism and desired sheet transport rate.

The effectiveness of the invention in pulling the receiver sheet 6 from the fusing roller 2 can be best understood by following a complete cycle of the source of varying potential 10. With no voltage applied to the member 8, there is no force of attraction between the member 8 and the receiver sheet 6. However, as the voltage applied to the member 8 by the source 10 increases towards its peak potential a force of attraction builds between the member 8 and receiver sheet 6 which overcomes the electrostatic attraction of the receiver sheet 6 for the roller 2. Ideally, the peak potential would be selected to occur just below the point when the air in the gap 14 breaks down, i.e., becomes substantially ionized due to the applied field since just below this point the maximum electrostatic force possible is obtained between the member 8 and receiver sheet 6. However, in actual practice, the breakdown point varies according to the humidity conditions, the insulating properties of the particular receiving sheet 6, and, most significantly, the amount of charge on the receiver sheet. The peak potential is, therefore, selected to obtain maximum attraction between member 8 and receiver sheet 6 under all operating conditions with the knowledge that there is likely to be a breakdown in the air gap 14 as the electric field approaches its peak potential. However, even if breakdown occurs, substantial current cannot flow between the conductive portion of member 8 and the receiver sheet 6, because of the dielectric material 12 coated on member 8. Only a displacement current, which is very low, flows to the surface of the dielectric coating 12 from the member 8 reducing the field in the air gap 14 without arcing. Once the point of breakdown is reached, the force of attraction between the receiver sheet 6 and member 8 collapses with the field. Thus, while breakdown causes a loss of pulling force on the sheet 6 for a short period of time, it is desirable to operate the apparatus of the invention with the peak potential at or above the breakdown point in order to achieve maximum pull just before breakdown occurs. The voltage of source 10 passes its peak, then decreases to zero completing its first cycle. Assuming a pulsed D.C. source is used, the cycle is repeated over and over again. The same pulling effect cannot be obtained with a constant potential because the voltage would have to be set at a point so low that no breakdown would occur under any conditions.

As noted above, no arcing can occur between the member 8 and the receiver sheet 6. If arcing occurred, the receiver sheet 6 would charge to the approximate potential of member 8 generating an electrostatic force between the receiver sheet 6 and the backing roller 4 or fusing roller 2. This electrostatic force would tack the receiver sheet 6 to the roller 2 or 4, the opposite result of that which is desired.

If an AC. source is used as shown in the preferred embodiment, voltage of source 10 passes its peak, then decreases to zero as described above, completing its first half cycle and starts increasing to a peak of opposite potential. The electric field in the air gap 14 follows the potential of source 10, that is to say, it decreases to zero and then starts increasing with the direction of force lines reversed from those of the first half cycle. It is important to note at this point that a force of attraction will exist between the receiver sheet 6 and member 8 regardless of the direction of the field force lines as long as the sheet 6 and member 8 are at different relative potentials. The force between the member 8 and the receiver sheet 6 is, therefore, independent of the electric field polarity applied to the member 8. This increasing field also produces a building force of attraction which reaches its maximum just as the air in the gapil4 breaks down due to the field. As before, only a displacement current flows from the member 8 to the surface of dielectric coating 12 reducing the field in the air gap 14 without arcing. The voltage passes its peak and decreases to zero completing the first cycle. The process then starts all over again. From the foregoing, the advantageous effects of the invention are readily apparent. Apparatus is disclosed which removes an electrically charged receiver sheet 6, from a transport roller 2 by applying an electrostatic pull during each cycle ofa pulsed DC source of potential or during each half cycle of an AC. source of potential 10. The receiver sheet 6 is, therefore, positively stripped from the fusing roller without abrading the roller 2 or damaging the sheet 6 and without creation of toner dust problems in other portions of the machine. Proper location of the member 8 allows the stripping action to accurately position the receiver sheet 6 on the output conveyor so that the sheet exits from the machine without jamming.

The invention has been described in detail with reference to a preferred embodiment thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

I claim:

1. In a machine having means for transporting along a predetermined path, a sheet or web material of the type having a tendency to adhere to the transporting means and move in a different path under the influence of electrostatic charge on the material, a detacking apparatus comprising:

a. a member positioned in close proximity to the predetermined path and having an inner conductive portion and an outer insulating portion facing the material; and means for applying a source of periodically varying electrical potential to said conductive portion, said source being of a frequency such that at least one attractive field is created and dissipated between said member and the material as the leading edge of the material advances to a position along the predetermined path proximate to said member, the peak strength of said field being sufficient to overcome the electrostatic attraction of the material for said transporting means.

2. In apparatus for advancing a flexible sheet or web material along a predefined path, such apparatus comprising a pair of rotatably mounted transport rollers having parallel axes of rotation and being arranged to cooperate with each other during the rotation thereof to advance the material through a nip formed by the curved surfaces of such rollers and means for preventing the material from becoming wrapped about one of the transport rollers upon being advanced through the nip formed by such rollers, the improvement wherein said preventing means comprises:

a. an elongated conductive member positioned substantially parallel to the axes of rotation of the transport rollers and in close proximity to the roller surface upon which the leading edge of the material has a tendency to adhere upon passing through the nip, said member having an outer coating of a dielectric substance; and

b. means for applying an AC potential to said conductive member to intermittently attract the material toward said conductive member.

3. The apparatus as defined in claim 2 wherein said coating of a dielectric substance is approximately 0.001 to 0.1 inch in thickness.

4. The apparatus as defined in claim 2 wherein the electrical potential applied to said conductive member by said means for applying an AC potential ranges from 0 to 12 kilovolts.

5. The apparatus as defined in claim 2 wherein the peak voltage of said AC potential is sufficient to substantially ionize the air in the nip but is insufficient to produce arcing between said conductive member and the material.

6. In combination with transport means for moving a sheet or web material electrostatically attracted thereto, improved apparatus for removing such material from the transport means, said apparatus comprising:

a. a conductive member having an outer coating of dielectric substance and being located in close proximity to such material; and

b. means for applying an alternating electrical potential to said conductive member to periodically create an attractive field between said member and the material sufficient to overcome the electrostatic attraction of the material for the transport means, the maximum potential difference-applied between said conductive member and the material by said potential applying means being sufficient to ionize the air in the gap between said member and the material but insufficient to produce arcing between said member and the material. 

1. In a machine having means for transporting along a predetermined path, a sheet or web material of the type having a tendency to adhere to the transporting means and move in a different path under the influence of electrostatic charge on the material, a detacking apparatus comprising: a. a member positioned in close proximity to the predetermined path and having an inner conductive portion and an outer insulating portion facing the material; and b. means for applying a source of periodically varying electrical potential to said conductive portion, said source being of a frequency such that at least one attractive field is created and dissipated between said member and the material as the leading edge of the material advances to a position along the predetermined path proximate to said member, the peak strength of said field being sufficient to overcome the electrostatic attraction of the mAterial for said transporting means.
 2. In apparatus for advancing a flexible sheet or web material along a predefined path, such apparatus comprising a pair of rotatably mounted transport rollers having parallel axes of rotation and being arranged to cooperate with each other during the rotation thereof to advance the material through a nip formed by the curved surfaces of such rollers and means for preventing the material from becoming wrapped about one of the transport rollers upon being advanced through the nip formed by such rollers, the improvement wherein said preventing means comprises: a. an elongated conductive member positioned substantially parallel to the axes of rotation of the transport rollers and in close proximity to the roller surface upon which the leading edge of the material has a tendency to adhere upon passing through the nip, said member having an outer coating of a dielectric substance; and b. means for applying an AC potential to said conductive member to intermittently attract the material toward said conductive member.
 3. The apparatus as defined in claim 2 wherein said coating of a dielectric substance is approximately 0.001 to 0.1 inch in thickness.
 4. The apparatus as defined in claim 2 wherein the electrical potential applied to said conductive member by said means for applying an AC potential ranges from 0 to 12 kilovolts.
 5. The apparatus as defined in claim 2 wherein the peak voltage of said AC potential is sufficient to substantially ionize the air in the nip but is insufficient to produce arcing between said conductive member and the material.
 6. In combination with transport means for moving a sheet or web material electrostatically attracted thereto, improved apparatus for removing such material from the transport means, said apparatus comprising: a. a conductive member having an outer coating of dielectric substance and being located in close proximity to such material; and b. means for applying an alternating electrical potential to said conductive member to periodically create an attractive field between said member and the material sufficient to overcome the electrostatic attraction of the material for the transport means, the maximum potential difference applied between said conductive member and the material by said potential applying means being sufficient to ionize the air in the gap between said member and the material but insufficient to produce arcing between said member and the material. 